The present invention relates to the manufacture of filter mountpieces for filter tipped rod-shaped smokers' products, and more particularly to improvements in a method and apparatus for making composite or multiplex filter mouthpieces which contain several dissimilar filter rod sections. Still more particularly, the invention relates to improvements in a method and apparatus for monitoring and controlling the operation of machines for the production of composite or multiplex filter mouthpieces.
As a rule, composite filter mouthpieces are produced in a machine which, in certain respects, resembles a cigarette rod maker. The machine comprises a first unit which assembles groups of dissimilar filter rod sections and a second unit which converts groups of dissimilar filter rod sections and a web of wrapping material into a continuous filter rod which is thereupon severed at regular intervals to yield a succession of discrete filter mouthpieces. The length of filter rod sections is often monitored by photoelectric or analogous means wherein a source emits a beam of radiation which is directed against the filter rod and a transducer generates electrical signals which denote the degree to which various sections absorb radiation.
The dissimilar filter rod sections may consist of entirely different filter materials or they may consist of an identical base material (such as acetate fibers) but with the base material in one type of sections interspersed with granulae of activated charcoal or the like. It is also possible to assemble the filler of the filter rod of filter rod sections some of which constitute gaps, i.e., columns of air between neighboring rod-shaped sections consisting of solid filter material. Still further, such gaps can be filled with granulae consisting of a suitable absorbent material to constitute rod-shaped sections which resemble rods solely because they are confined by the tubular wrapper of the filter rod and are flanked by rod-shaped sections consisting of acetate fibers, crepe paper or the like.
An important requisite for the manufacture of satisfactory composite or multiplex filter mouthpieces for use in the making of filter cigarettes, cigars or cigarillos is that each mouthpiece should contain a predetermined length of each of two or more different types of filter material, e.g., a first section of predetermined length which consists of acetate fibers with a paper wrapper therearound, a second section of predetermined length which consists of crepe paper, and a third section of predetermined length which is a column of air between the first and second sections or is adjacent to one of the first and second sections (the third section may constitute a non-self-supporting column of charcoal granulae or the like). The length of various sections of a composite filter mouthpiece can deviate from a desired or optimum length for a number of reasons, e.g., due to improper timing of the severing action upon the filter rod or owing to improper assembly of filter rod sections into a rod-like filler which is to be draped into a web of cigarette paper, imitation cork or other suitable wrapping material (e.g., the improper assembly may result from lengthwise shifting of solid-rod-like sections with attendant reduction or increase of the width of the aforementioned gaps). When a filter mouthpiece is severed across the gap to yield two shorter mouthpieces, each gap is converted into two recesses which are adjacent to the free ends of the respective filter mouthpieces in filter cigarettes or the like. Improper spacing of solid filter rod sections in the filter rod entails changes of the length of recesses.
On the other hand, the quality of certain filter mouthpieces is not adversely affected by defects which are attributable to eventual clearances between neighboring solid filter rod sections, especially if the width of such clearances is not excessive. Heretofore known apparatus for monitoring composite filter rods are incapable of accurately ascertaining the width of the just mentioned clearances; therefore, such apparatus are designed to invariably segregate each and every filter mouthpiece wherein two solid rod-shaped filter rod sections do not abut against each other. This results in an excessive number of rejects and is also undesirable on the aforementioned ground, namely, that the presence of relatively narrow clearances between two solid rod-like sections of the filler of a filter mouthpiece does not render such mouthpiece defective or useless.
An apparatus for monitoring the gaps between neighboring cigarettes of a file of coaxial cigarettes is disclosed in U.S. Pat. No. 3,355,592 to Muir. The patented apparatus comprises a photodetector in circuit with a capacitor which completes the holding circuit of a relay when it accumulates a predetermined charge. The charge of the capacitor is a function of the ratio of the length of cigarettes to the width of gaps between neighboring cigarettes. When the width of the gaps decreases, the charge of the capacitor also decreases whereby the holding circuit of the relay opens. The accuracy of the just described apparatus is very low and, furthermore, the apparatus can detect only a reduction of the width of gaps but is incapable of indicating whether or not the width of the gaps is excessive. Therefore, such apparatus cannot be used in a machine for the production of composite filter mouthpieces because the manufacturer is concerned primarily with detection of those filter mouthpieces wherein the width of the gaps is excessive. At the very least, the manufacturer wishes to ascertain those filter mouthpieces wherein the width of the gaps is insufficient as well as to pinpoint those mouthpieces wherein the width of the gaps is excessive.